The present invention relates to a process and device for the suspension smelting of finely-divided sulfidic or oxidic and sulfidic ores and concentrates.
The suspension smelting of sulfidic concentrates, based on U.S. Pat. No. 2,506,557 has been increasingly adopted all over the world. It is known to be economical in terms of energy and, furthermore, it is a smelting process friendly to the environment. This so-called autogenic flash smelting process is, however, nowhere fully autogenic, i.e., operating without external fuel, but large quantitites of fuel, usually oil, must be used at different points of the flash smelting furnance. The flash smelting process is well known and has been described in several articles (e.g., Journal of Metals, June 1958, Petri Bryk, John Ryselin, Jorma Honkasalo, Rolf Malmstrom: "Flash Smelting Copper Concentrates" and "The First International Flash Smelting Congress, Finland, October 23-27, 1972").
Described briefly, the process is as follows. Dried, finely-divided concentrate plus the circulating flying dust and possible slagging agents and air and/or oxygen mixture, preheated or cold, are fed downwards into a vertical flash smelting furnance reaction shaft, where the oxidation reactions occur in suspension at a high temperature. Under the effect of the heat of reaction and the possible additional fuel, most of the reaction products smelt (with the exception of certain slag components). When copper concentrates are concerned, the following sum reactions can be thought to occur in the reaction shaft: EQU 2 CU FeS.sub.2 .fwdarw. Cu.sub.2 S + 1/2 S.sub.2 + 2 FeS EQU cu.sub.2 S + 1 1/2 O.sub.2 .fwdarw. CU.sub.2 O + SO.sub.2 EQU feS.sub.2 .fwdarw. FeS + 1/2 S.sub.2 EQU 1/2 s.sub.2 + o.sub.2 .fwdarw. so.sub.2 EQU feS + 1 1/2 O.sub.2 .fwdarw. FeO + SO.sub.2 EQU 3feO + 1/2 O.sub.2 .fwdarw. Fe.sub.3 O.sub.4
similar reactions occur in the case of other concentrates. The suspension falling from the reaction shaft arrives in the horizontal furnance part, the so-called lower furnance or settler, where there are at least two but sometimes three different melt layers. The lowest one can be a metal layer, usually blister copper, with either a matte layer or directly a slag layer on top of it. Usually the lowest is a matte layer with a slag layer on top of it. Most of the melt and solid particles in suspension fall directly into the melt which is below the reaction shaft, at approximately the slag discharge temperature, and the most finely divided part continues along with the gases to the other end of the furnace. On the way, suspension keeps falling into the lower furnace. At its other end the gases are directed straight upwards along the rising shaft and further on to the gas treatment devices, the waste heat boiler and the electric filter. Usually the aim is to perform the smelting as autogenically as possible, without outside fuel. For this purpose, air is preheated and/or oxygen-enriched in the reaction shaft.
When using conventional sulfide concentrates which contain chalcopyrite, pentlandites, pyrites and other sulfides of iron, it has been noted that the oxidation of iron in the reaction shaft does not result in the formation of the desired FeO but the reactions continue as far as Fe.sub.3 O.sub.4.
The higher the grade of matte desired in the smelting, that is, the further the concentrate is oxidized in the reaction shaft at the temperatures in question, the higher the degree to which the oxidized iron is in the form of magnetite, Fe.sub.3 O.sub.4, in the lower part of the reaction shaft. Oxides of other metals can also be produced. In any case, an equivalent quantity of iron sulfide, FeS, or other metal sulfides remains unoxidized. The final reactions occur almost solely after the particles have fallen into the melt in the lower furnance, and the desired matte and/or metal and slag phases are thereby produced. The following reactions are possible: EQU Ia: 3Fe.sub.3 O.sub.4(s) + FeS.sub.(2) .fwdarw. 10FeO.sub.(s) + SO.sub.2(g) EQU .DELTA.H.degree..sub.1300.degree. .perspectiveto. + 398 kJ EQU ib: 3Fe.sub.3 O.sub.4(1) + FeS.sub.(a) .fwdarw. 10FeO.sub.(s) + SO.sub.2(g) EQU .DELTA.H.degree..sub.1300.degree. .perspectiveto. - 16 kJ EQU ii: 2feO.sub.(s) + SiO.sub.2(g) .fwdarw. 2FeO .multidot. SiO.sub.2(2) EQU .DELTA.h.degree..sub.1300.degree. .perspectiveto. +73.5 kJ EQU iii: cu.sub.2 S.sub.(2) + 2Cu.sub.2 O.sub.(2) .fwdarw. 6Cu.sub.(2) + SO.sub.2(g) EQU .DELTA.H.degree..sub.1300.degree. .delta. +76.2 kJ EQU iv: 3cu.sub.2 o.sub.(2) + feS.sub.(2) .fwdarw. 6Cu.sub.(2) + FeO.sub.(s) + SO.sub.2(g) EQU .DELTA.H.degree..sub.1300.degree. .delta. -35 kJ EQU v: cu.sub.2 O.sub.(2) + FeS.sub.(2) .fwdarw. FeO.sub.(s) + Cu.sub.2 S.sub.(2) EQU .DELTA.h.degree..sub.1300.degree. .perspectiveto. -115kJ EQU ia+II: 3Fe.sub.3 O.sub.4(s) + FeS.sub.(2) + 5SiO.sub.2(s) .fwdarw. 5(2FeO .multidot. SiO.sub.2).sub.(2) +SO.sub.2(g) EQU .DELTA.H.degree..sub.1300.degree. .perspectiveto. +766 kJ EQU ib+II: 3Fe.sub.3 O.sub.4(1) + FeS.sub.(2) + 5SiO.sub.2(s) .fwdarw. 5(2FeO .multidot. SiO.sub.2(2) + SO.sub.2(g) EQU .DELTA.H.degree..sub.1300.degree. .perspectiveto. +352 kJ
in a normal copper smelting process the most important factor in terms of heat economy is the combination of the reduction and slagging reactions (Ia+II or Ib+II). Significant quantities of copper oxidule, Cu.sub.2 O, will not begin to appear in the lower part of the reaction shaft until the aim is a matte with a copper concentration of more than 75% Cu or metallic copper. Even then, however, the magnetite must be reduced sufficiently so that the copper losses into the slag will not be immoderate. Thus, the reaction I+II is always significant. Other reactions occur to a small degree, but they are not very important in terms of heat economy. Besides these endothermal reactions there are thermal losses in the lower furnace as well.
According to current practice, oil, gas or coal is burned both below and along the reaction shaft to generate heat for the lower-furnace reactions and to replace the thermal losses. Under the reaction shaft, where the endothermal reactions occur, the melt is well mixed owing to the generating SO.sub.2 gas, and the transfer of heat is effective, but elsewhere in the furnace, where the slag is almost stationary, the transfer of heat is poor. It has been verified by measurements that in such a stationary slag the temperature difference is 5.degree.-10.degree. C/cm. If the slag discharge temperature is 1250.degree.-1300.degree. C., its surface temperature can easily be 100.degree. C. higher. Transfer of heat from the combustion gases through the slag is difficult because of the high surface temperature of the slag and because of counterradiation. The entire gas quantity must be heated to a high temperature and the thermal losses in the part above the furnace melt are great. Thus, the gas quantity increases and expensive gas treatment devices, such as waste heat boiler, electric filter, blowers, must accordingly be dimensioned large.
The object of the present invention is to eliminate the above drawbacks and to produce a process and device for the suspension smelting of finely-divided sulfide or oxide and sulfide ores and concentrates, wherein a suspension of a finely-divided raw material in air and/or oxygen is directed downwards in the reaction shaft formed by the suspension and the melt below it in order to oxidize and partially smelt the raw material in suspension, whereafter the suspension flow is caused to change its flow direction perpendicularly sidewards so that most of the raw material particles contained in the suspension flow impinge against the surface of the accumulated melt in the lower part of the suspension reaction shaft, and the remaining suspension flow is directed into the rising-flow shaft, where it is possibly after-sulfidized and cooled and the solids are separated from the remaining suspension flow and possibly returned to the reaction zone.